The present invention relates generally controlling electro-pneumatic braking on railway train of railcars having electrically controlled pneumatic (ECP) brake equipment, and more particularly to a method and apparatus for controlling the braking on such ECP equipped railcars from an automatic brake control valve on a locomotive of the train, which automatic brake valve conventionally controls the train brakes pneumatically via a brake pipe interconnecting the locomotive and the railcars. An example of such an automatic brake valve is a Type 26 automatic brake valve manufactured by Westinghouse Air Brake Technologies Company (“WABTEC”™), or other types of locomotive brake control valves which operate in the same general manner. Controlling the application of brakes on ECP equipped railcars using a conventional automatic brake valve provides a manner of control which is similar in appearance and operation to existing pneumatic braking equipment from the train operator's standpoint, while incorporating the advantages of ECP braking, as discussed in detail hereinafter.
The existing standard method of controlling air brakes on trains using an automatic brake valve involves pressurizing a fluid passageway, and its associated connectors and fittings, known collectively as the brake pipe, to which the locomotive and each railcar is interconnected. In particular, such automatic brake valves can operate the train brakes by the train operator initiating pressure changes in an equalizing reservoir via the automatic brake handle, or other automatic brake valve operator interface. The pressure change in the equalizing reservoir, or a similar pressurized control volume, can be mirrored in the brake pipe by a relay valve, which is typically a portion of the automatic brake valve. The pressure change in the brake pipe is then detected by brake equipment on each railcar, which is connected to the brake pipe, and used to control the level of braking on the railcar. Conventionally, each railcar has equipment for applying the brakes, including an air reservoir which is typically divided into two portions—an emergency portion and an auxiliary portion, and a pneumatic brake control valve for applying and releasing the brakes on the railcar. One such railcar brake valve is, for example, an ABDW™ valve manufactured by WABTEC™. However, it should also be understood that there are other types of railcar brake control valves besides the ABDW™ which operate in the same general manner. The such railcar brake control valves can typically have a service portion—for service level brake applications, and an emergency portion—for emergency brake applications. The auxiliary and emergency reservoirs are normally charged from the brake pipe to a predetermined pressure, which is set by the train operator, using what is commonly referred to as the “feed valve.” Once the brake pipe on a train has been charged to the feed valve setting, the brake equipment of the controlling locomotive, when so equipped, will maintain the desired pressure against slight to moderate leakage.
In order to apply the brakes on the train, the operator typically uses an interface, or control portion of the automatic brake valve, which is typically the brake handle, but could be any other type of operator control portion or device, to reduce the pressure in the brake pipe by a selected amount. A low to moderate reduction of pressure in the brake pipe will cause the service portion or the railcar brake control valve to admit air from the auxiliary reservoir into the brake cylinder, in proportion to the amount of reduction in brake pipe pressure, to apply the brakes on the railcar. Subsequent reductions in brake pipe pressure will cause greater brake cylinder pressure, up to the point at which the pressure in the auxiliary reservoir is permitted to equalize with the pressure in the brake cylinder. If a greater amount of brake cylinder pressure is desired, the brake pipe pressure can be rapidly reduced to zero, which will cause the railcar brake control valve emergency portion to add the volume of the emergency reservoir to the combined auxiliary reservoir and brake cylinder pressure.
Due to the design of freight car brake equipment, as well as the properties of compressed air in the brake system, an incremental, or “graduated” release of the brakes on a freight train is not possible. The operator can release the brakes on the each railcar only by moving the handle of the automatic brake valve to the “release” position, thereby restoring the pressure in the brake pipe to the previously established feed valve setting. In response to the rise in brake pipe pressure, the brake control valves on the each railcar will vent the brake cylinder to release the pressure, and also couple the auxiliary and emergency reservoirs to the brake pipe to restore the pressure in each reservoir to the desired setpoint.
It should be understood that the movement of pressurized air within the brake pipe is typically restrained by various factors, such as bends, branch pipes, rubber hoses, couplings, and the like. Therefore, upon initiation of a brake application by the train operator, via a reduction in brake pipe pressure, a lengthy delay may occur until the brakes at the rearmost railcars of the train begin to develop significant braking effort. As a result, an unequal application of the brakes occurs through the train, due to the amount of time it takes for the pressure reduction in the brake pipe to propagate through the brake pipe from the locomotive to the rearmost railcars in the train. A consequence of non-uniform braking on the railcars from front of the train to rear is that serious tensile or compressive forces can be generated in the train, which can cause serious train handling problems.
Similarly, when releasing the brakes following an application, air must flow into the brake pipe from the front of the train, and release of the brakes on each railcar occurs, like the brake application process described above, in a sequential manner, rather than simultaneously as would be preferred. Again, serious consequences may result from the thus generated in-train forces, especially at slow speeds.
In order to eliminate several of the perceived shortcomings of the conventional pneumatically implemented train braking control system, an ECP brake system has been developed by which each railcar can develop truly simultaneous brake applications and releases through the use of a cable, commonly called a trainline, connected between the various cars of the train. Alternatively to the use of a trainline, radio communication control could be utilized between the locomotives and the railcars. The trainline can provide two functions: 1) a source of current from which the electronic equipment on each car can charge local batteries, and 2) a pathway by which electrical control signals can be communicated to cars and other locomotives so equipped.
In the ECP braking system, trains made up of cars and locomotives so equipped can operate in such a fashion that the brake pipe no longer serves as both a supply and control line, but becomes only a means by which air is supplied to the cars for charging their reservoirs and supplying brake cylinder pressure. Applications of the brakes on the cars can instead be accomplished by means of an electrical signal on the trainline, or by radio communication. Each railcar, and additional locomotives when used, in the train can receive command signals and apply or release the brakes on the car according to the level of braking communicated in the command signal.
Since all of the brakes on the train will apply in parallel, rather than serially, smoother handling of the train can be achieved with less chance of damage to the train or its cargo. A second benefit of the ECP system is that the brake cylinder pressure on the various railcars can now be released in incremental steps. This graduated release allows the train operator to gradually reduce the braking effort on the train without danger of having the train pick up excessive speed from having to fully release the brakes on all of the railcars.
Presently known ECP system are fully electronic, using components such as magnet valves and transducers to develop the required level of air pressure in the brake cylinders. The existing brake equipment in conventional locomotives, i.e., non-electronic brake control valves, operates by controlling air pressure mechanically. Therefore, for conventional brake control equipment in locomotives to be able to control the brakes on ECP equipped railcars, an additional piece of equipment, called a Head End Unit (HEU), it typically added to permit the train operator to control braking on the railcars. However, the HEU competes with space in the already crowded locomotive cab. To control ECP braking on the railcars, such HEUs typically includes a variety of push-button controls, requiring the train operator to use this additional train brake control device to operate the brakes on the railcars in ECP mode. This is also in contrast to the movement of the brake handle typically used on conventional non-electronic locomotive automatic brake control valves to which the operator is accustomed.
Accordingly it would be desirable to provide a brake control system which permits a train operator to control the brakes on the railcars in an ECP manner using the existing pneumatic locomotive brake control valve. Moreover, the brake handle commonly used with such brake valves, with which the train operator may be comfortable, can also be used to control the ECP braking on the railcars, thus integrating the operation of the ECP braking system with the conventional pneumatic locomotive brake control valve such that an additional ECP brake control device is not required.